Disk drive devices using various kinds of media, such as optical disks, magneto-optical disks, flexible magnetic disks, and the like, have been known in the art. In particular, hard disk drives (HDDs) have been widely used as storage devices of computers and have been one of the indispensable storage devices for current computer systems. Moreover, HDDs have found widespread application to moving image recording/reproducing apparatuses, car navigation systems, cellular phones, and the like, in addition to the computers, due to their outstanding characteristics.
A magnetic disk used in an HDD has multiple concentric data tracks and servo tracks. Each servo track contains multiple servo data having address information. Each data track includes multiple data sectors containing user data recorded thereon. Data sectors are recorded between servo data discrete in the circumferential direction. A head element portion of a head slider supported by a swinging actuator accesses a desired data sector in accordance with address information in the servo data to write data to and retrieve data from a data sector.
In order to increase the storage capacity of an HDD or to improve the reliability of an HDD, it has been proposed to specify a data track pitch for each head (each recording surface). Specifying the data track pitch so as to match head characteristics such as a read width or a write width leads to suppression of adjacent track interference (ATI) in data write and increase in data capacity per recording surface.
Two approaches have been proposed to adjust the data track pitch for each recording surface. One is a method to make servo tracks conform to data tracks and adjust the servo track pitch for each recording surface in the servo track write (refer to Japanese Patent Publication No. 2006-114142 “Patent Document 1”, for example). The other is a method to provide servo tracks with a common pitch to all recording surfaces and adjust the data track pitch for each recording surface.
In specifying a data track pitch, it is preferable that the data track pitch be as narrow as possible for data capacity while it is preferable that the data track pitch be as wide as possible for the reliability against ATI. Writing a data track in a too narrow data track pitch causes partial erasure of adjacent data tracks so that the adjacent data tracks cannot be accurately read. This is called a squeeze error.
The method disclosed in Patent Document 1 writes a test pattern, and writes adjacent test patterns at the adjacent positions thereto. Then, it measures the error rate of the prior written test pattern. It sequentially writes test patterns while decreasing the data track pith, measures error rates of the test patterns, and determines the narrowest data track pitch at which the error rate satisfies criterion. It specifies the data track pitch to be optimum.
The above method can specify an appropriate data track pitch if ideal accuracy is realized in head positioning. However, an HDD as a product permits changes in head position during a following operation. The HDD continues writing data while the head is positioned within a specific range from the target position, but stops writing data when the head is positioned away from the specific range.
In this manner, the head is always changing its position in the radial direction during data write and the position of the head in the radial direction changes with a certain sigma. Therefore, the error rate measured in the test is not always achieved in actual operation of the HDD and a higher error rate than the one in the test may be exhibited in the HDD as a product due to the changes in head position. In other words, a squeeze error possibly occurs.
Accordingly, in manufacturing of HDDs, it is necessary to specify the data track pitch in consideration of changes in head position in the data write. It is necessary to specify the optimum track pitch without excess or deficiency to increase data capacity without causing a squeeze error in expected changes in head position.